XI V] NERVE FIBRES 109 



5. Take another piece of fresh nerve, and place it 

 in a small quantity of osmic acid '5 p.c. for to ^ an 

 hour, covering it up to prevent evaporation. Wash it 

 in water, place it in dilute glycerine for a minute or 

 two. Remove to a slide and tease. Select a small 

 bundle separated from the connective tissue sheath, 

 and put the rest back in glycerine for use if required. 

 Tease further the small bundle, and arrange the fibres 

 parallel to one another; place a small drop of dilute 

 glycerine on the centre of a cover-slip, and mount. 



Select a nerve fibre which is isolated for a con- 

 siderable part of its length, and observe 



The medullary sheath, stained black with osmic 

 acid. 



The nodes ; note that the distance between two 

 successive nodes is greater in large than in small nerve 

 fibres. 



The numerous oblique breaks in the medulla, 

 dividing it into short overlapping cylinders. 



The nuclei of the sheath; there is one to each 

 internode about halfway between the two nodes, it is 

 an inconspicuous transparent elongated body, usually 

 projecting into the medulla. 



The nuclei of the sheath may be stained by placing a piece of the 

 nerve, after brief treatment with osmic acid, in picrocarmine or in 

 haematoxylin for an hour. In the former preparation, the cells of the 

 tine connective tissue around the nerve fibres will also be well seen. 



6. Transverse sections in paraffin of a large nerve 

 stained with picrocarmine (potassium bichromate 2 p.c.). 

 Mount in balsam. Observe 



The epineurium surrounding the whole nerve and 



